Introduction

Skeletal muscle comprises the largest group of tissues in the human body and accounts for up to 40% of total body weight. This type of muscle, which is innervated by the somatic nervous system, is under voluntary control. Skeletal muscle performs many important functions in the body, including:

• Movement of body parts

• Heat production

Most skeletal muscles are attached to bones, which enables them to control body movements, such as walking. These muscles are also responsible for the manipulation of objects, such as writing with a pencil or eating with a fork. Furthermore, eye movement is carried out by several pairs of skeletal muscles. Finally, the contractions of certain groups of muscles referred to as "antigravity" muscles are needed to maintain posture and provide body support. Only about 20 to 30% of the nutrient energy consumed during skeletal muscle activity is actually converted into purposeful work. The remaining 70 to 80% is given off as heat. Therefore, because of its large mass, skeletal muscle is the tissue most responsible for maintaining and increasing body temperature. Although it typically occurs subconsciously, breathing is a voluntary activity. The diaphragm and other muscles of inspiration and expiration are skeletal muscles. As such, breathing can be voluntarily controlled to some extent (see Chapter 17). Speaking, and other forms of vocalization, depend upon the coordinated contraction of skeletal muscles.

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.